It’s a warm day in Mountain View, and just outside the Computer History Museum, Lexus SUVs are pulling up to the curb. The Lexus RX450h is a beautiful car, but today my eye travels immediately to its roof, where an attached laser radar array is spinning at 10 times per second.

At around $70,000, the laser array is more valuable than the vehicle itself. A pair of test drivers invites me to climb in the back. I’m about to take a ride in Google’s self-driving car.